Strip processing



G. P. wlLsoN I 2,407,120

Sept. 3, 1946.

IP PROCESS ING F iled May 22, 1944 INVENTOR. G'OIderP W801:

Patented Sept. 3, 1946 STRIP PROCESSING Golder P. Wilson, Alton, Ill., assignor to Olin Industries, Inc., a. corporation of Delaware Application May 22, 1944, Serial No. 536,752

6 Claims. 1

This invention relates to the heating of metal strip by means of electric induction.

It has heretofore been Well known that the heating of metal can be accomplished by electric induction by employing the transformer principle in which a rimary coil is supplied with an alternating electric current, and the work, or metal to be heated, when placed in inductive relationship with the primary coil, is heated by its resistance to the induced electric or magnetic current.

Various methods and apparatus have been described heretofore for bringing the metal into inductive relationship with the primary coil. For instance, in one method for treating metal strip, a length of the strip was rolled up to provide a ring formed of several layers of the strip and the ring was then heated by the current induced therein from a surrounding primary coil. Such methods and apparatus have the disadvantages of being limited to intermittent operation, and in the case of very thin wide strip, the individual layers in the ring tend to become warped at the higher temperatures due to their own weight, and owing to the large cross section of the ring formed by the layers of strip, a current of very high amperage must be induced in order to bring the ring to the effective temperature.

In another method, the strip was continuously passed in an axial direction through a primary coil, the metal being heated by the locally induced magnetic and electric eddy currents. Such methods and apparatus have the disadvantage that with high conductivity non-magnetic strip it is diificult to induce electrical eddy currents of sufficient magnitude to bring the strip to an effective treating temperature.

According to other methods, the metal in the form of wire, or coiled rod, was fed in the paths of a helix around, or through, a primary coil, but such methods and apparatus have among others the disadvantage of not being suitable for use with wide strip, due to the difliculty involved in forming such strip into a helix.

According to still another method for heating offered by such contact bars, and, in some instances the contact parts are subject to excessive wear requiring frequent replacement.

All such prior methods and apparatus for the electric induction heat-treating of metal have been attended by one or more serious disadvantages and it is an object of this invention to provide an improved method and apparatus overcoming all such objections.

Another object of this invention is to provide an improved method and apparatus for the efficient and economical continuous heating of metal strip by electric induction.

Another object of the invention is to provide an improved. process and an eiiicient electric induction furnace for economically effecting the continuous heat treatment of metal strip having either high or low electrical conductivity.

, Still another object of the invention is to provide an improved process and an electric induction furnace suitable for the heating of a nonmagnetic metal such as a copper alloy in the form of strip.

Other objects and advantage will become apparent from the description and accompanying thus forming a secondary or complete electric circuit from the metal strip itself, with heating being effected by the resistance of the metal to the current induced in the loop.

Referring to the drawing, the metal strip l is unwound from the coil of metal strip 2, passes over support roll 5, through th laminated iron core 6 with primary coil 1 having leads 8 and 9, passes over support roll [0, around and in contact with the outer layer of metal strip I in coil 2, and is wound up into coil II on support roll or reel 12 which is driven by motor l3. The support roll or reel 3 for coil 2 may be coupled to a motor or dra enerator such as illustrated at 4. In passing around the coil 2, the wide surface of the strip I is in contact with the outer layer of the coil 2 and is bent around a substantial portion of the surface of the coil 2 so that a large area of contact is provided with a good electrical connection and low amperage per square inch between the strip 1 and the outer layer of coil 2 3 to prevent arcing and burning. A complete secondary electric circuit is thus provided by the moving strip I around the primary coil I.

An alternating electric current, which may be of either high or low frequency or, for instance, any of the available standard commercial frequencies, is applied to the primary leads 8 and 9, and the strip is heated by the current induced in the loop. The temperature of the strip can be regulated either by varying the speed at which the strip travels or b varying the power supplied to the primary coil I, The core 6 may be mounted on any suitable support and the rollers 3, 5, I and I2 may likewise be mounted on any suitable support. If the rollers 3, and ID are made of metal or other electrical conductors, care must be taken to avoid providing any electrical connection between them through their supports, since the induced current may then flow through the supports instead of being confined to the strip I. Such short circuiting can be avoided with metal rolls in any of the well known ways, for instance, by supplying the rolls with bearings made of an insulator or by providing separate supports or supports made of an insulator. It is preferred, however, to form the rolls themselves from an insulator.

If desired, spray systems, such as illustrated at I4 and I5, may be employed to spray fluid on the strip I for cleaning or temperature controlling purposes. For instance, the spray system at I5 may be employed to cool the strip I prior to contact with the coil 2. In operation, the portion of the strip I brought in contact with the coil 2 is preferably maintained at the same temperature as the outer layer of the coil 2, so that there will be no tendency for the loop formed of strip I to continuously increase in size.

Any other suitable means may be employed for supplying the alternating electromagnetic field. For instance, the primary induction means may consist of a primary coil I wound about a leg of the core 6 outside the loop of strip, or may consist of a coreless primary coil disposed within the loop of strip.

' In accordance with this invention magnetic or nonmagnetic metal of either high or low electrical conductivity may be continuously heated in the form of fiat strip having any desired width, Likewise, the heating may be accomplished by applying current to the primary coil of any desired frequency within practical limits.

When the coil 2 is completely unwound, a new coil is inserted on the roll or reel 3 and the strip is again threaded through the furnace, or if desired, suitable stitching apparatus may be employed for fastening the end of the strip from coil 2 to the end of the strip from the new coil so that a strip is fed through the furnace without interruption. Good electrical connection between the strip I and the coil 2 is provided, since the strip I and the outer layer of coil 2 are constantly changing their contact surface, and little or no oxidation can take place to increase the electrical resistance at these points of contact, The strip after passing over coil 2 can, if desired, be passed through a quenching or pickling tank before being wound up again on coil II. In annealing metal strip, it is desirable to obtain annealed strip having a certain degree of hardness and this can be readily accomplished by changing either the speed of travel of the strip or the power input to the primary, or both, until the temperature and time of treatment necessary for the desired strip hardness is obtained.

Due to the proximity of the secondary loop and the primary coil 1 and the good electrical connection between the strip I and the coil 2, a very high power factor may be obtained, for instance 6 as high as 0.90 or higher. If it is desired, for instance, to bright anneal brass, this may readily be accomplished by enclosing the furnace in a housing supplied with an inert atmosphere in the usual manner, If no such housing is used, any oxide film or discoloration, which may form on the strip at the annealing temperature employed, -may be readily removed by passing the strip through an acid pickling solution.

In addition to annealing treatments, this invention is applicable to other heat treatments, for instance, it may be used for normalizing, quenching, and drawing of steel strips, for the reflowing of tin on iron strip, for making copper clad steel sheets or other laminated sheet, and the like.

The heating unit can be-made relatively small and simple and sturdy in construction. The invention accordingly provides for the economical, continuous heating of metal in strip form and has a wide field of utility without being subject to all the disadvantages obtained with prior processes and apparatus.

It is understood that the embodiments of the present invention as shown and described are only illustrated and, that the scope of the invention is not to be limited thereby except insofar as is defined in the following claims.

Having thus described the invention, what is claimed and desired to secureby Letters Patent is:

1. In an electric inductionfurnace, the combination which comprises an alternating electromagnetic field, means for unwinding metal strip from a coil, means for advancing said strip through said alternating electromagnetic field, and means for bringing said strip and said coil together to provide an electrical contact therebetween.

2. In an electric induction furnace, the combination which comprises a primary induction means, means for unwinding metal strip from a coil, means for advancing said strip around and in inductive relation to the primary induction means, and contacting means for bringing said strip and said coil together to provide an electrical contact therebetween.

3. In an electric induction furnace, the com bination which comprises means for unwinding metal strip from a coil thereof, means for holding said moving strip out of contact with said coil, means for bringing said strip and said coil together again to provide an electrical contact therebetween, and means for inducing an electric current in the electrical loop formed by said strip and said coil.

l. In an electric induction furnace the combination which comprises means for unwinding metal strip from a coil thereof, means for holding said moving strip out of contact with said coil, roller means for bringing said moving strip and said coil together again to provide an electrical contact therebetween, and means for inducing an electric current in the electrical loop formed by said strip and said coil.

5. In an electric induction furnace for heating metal strip the combination which comprises a support roll for holding a coil of metal strip, means for unwinding the strip from said coil, a primary induction means, support rolls for guid- 75 ing said moving strip around and in inductive ing said moving metal strip around and in inductive relation to said primary induction means, roller means for bringing said strip and said coil together again after said strip has passed around said primary induction means, means for cooling said strip before it is again contacted 'With said coil, and means for supplying an alternating electric current to said primary induction means.

- GOLDER P. WILSON. 

